system for controlling fuel, metering into an internal combustion engine

ABSTRACT

A system for controlling fuel metering into an internal combustion engine, in particular a self-igniting internal combustion engine, is described. An electromagnetic valve influences the beginning and/or the end of fuel metering. An inductive pressure sensor is provided, which generates a signal corresponding to the pressure in a high-pressure area.

BACKGROUND INFORMATION

The present invention concerns a system for controlling fuel meteringinto an internal combustion engine.

Such a system for controlling fuel metering into an internal combustionengine is known from DE-OS 35 40 811, where a process and a device forcontrolling fuel metering into an internal combustion engine, inparticular a self-igniting internal combustion engine, is described. Thefuel metering system described therein is referred to as a pump-nozzlesystem, where a cam shaft drives a pump piston in a pump cylinder. Anelectromagnetic solenoid valve controls the fuel flow to an elementspace depending on a variety of operating parameters. The pressure inthe element space is not measured in this device; therefore accuratefuel metering is not possible.

Furthermore, DE-OS 34 26 799 (U.S. Pat. No. 4,653,447) discloses aprocess and a device for controlling fuel metering, where the beginningand the end of fuel delivery can be controlled using a solenoid valve.The beginning and the end of fuel delivery, determined by the solenoidvalve, is detected by the variation of the flow through the solenoidvalve.

SUMMARY OF THE INVENTION

With the procedure according to the present invention, accurate controlof fuel metering into an internal combustion engine is possible.

This advantage is achieved at a low cost; in particular, no additionallines or cable connections are required between the fuel metering unitand the control.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a fuel metering system according to thepresent invention.

FIG. 2 shows a circuit block diagram of a fuel metering device accordingto the present invention.

FIG. 3a shows a graph of current over time in the fuel metering deviceaccording to the present invention.

FIG. 3b shows a graph of the derivative of current over time in the fuelmetering device according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The process according to the present invention is explained below usingthe example of a pump-nozzle unit. The process according to the presentinvention is not limited, however, to this application. It can be usedin any fuel metering system where an inductive sensor, in particular apressure sensor, and an electromagnetic valve are used. This can also bethe case, for example, in solenoid valve-controlled distributor pumpsand common rail systems. The process according to the present inventioncan also be used with systems where the electromagnetic valve determinesonly the beginning or only the end of metering.

FIG. 1 shows the device according to the present invention forcontrolling fuel metering as a simplified block diagram. Anelectromagnetic solenoid valve 100, comprising a coil 105, providescommunication between an element space 110, which can also be referredto as the high-pressure area, and a low-pressure area. A fuel deliverypump 115 delivers fuel from a fuel storage container 120 into thelow-pressure area.

Element space 110 is formed by a pump cylinder. A pump piston 125 isarranged in pump cylinder 122. Pump piston 125 is driven by a cam 130,which is driven by a shaft. Pump piston 125 and an injection valve 135delimit element space 110. A pressure sensor 140, comprising a coil 145,is arranged in element space 110.

This device operates as follows. Fuel delivery pump 115 delivers fuelfrom storage container 120 into element space 110. Cam 130, drivendirectly by a shaft, for example, the cam shaft of the internalcombustion engine, drives pump piston 125. Pump piston 125 moves up anddown depending on the position of cam 130. During its downward movement,the fuel in element space 110 is pressurized by pump piston 125. When acertain pressure is reached, injection valve 135 opens and the fuel isinjected through injection nozzle 135 into the combustion chamber of theinternal combustion engine.

Pressure can only build up in element space 110 when solenoid valve 100is closed. If solenoid valve 100 is open, pressure cannot build up andtherefore injection is impossible. The beginning and the end of fueldelivery can be controlled by opening and closing solenoid valve 100.When the solenoid valve opens or closes, the inductance of coil 105changes. This change in the inductance of coil 105 can be detected byanalyzing the current variation.

Pressure sensor 140 measures the pressure in element space 110. It isprovided according to the present invention that when a predefinedpressure is reached, the pressure sensor generates a signal. For thispurpose, the pressure sensor is designed so that when a pressurethreshold is reached, the inductance of coil 145 changes. Pressuresensor 140 is, for example, a type of barometric box integrated in thepump-nozzle unit. When a pressure threshold is reached, a magneticallyconductive armature moves in the coil, resulting in a change in theinductance of coil 145.

It is provided according to the present invention that coil 145 ofpressure sensor 140 and coil 105 are connected in series. By measuringthe overall inductance, both the change in inductance of pressure sensor140 and the change in the switching state of solenoid valve 100 can bedetected. By connecting the solenoid valve winding and the pressuresensor in series, no additional connections are required on thepump-nozzle unit. Furthermore no additional cables are necessary betweenthe pump-nozzle unit and a controller.

FIG. 2 shows the electric wiring of the different elements. Elementsdescribed in FIG. 1 are denoted by the same numbers. Coil 105 ofsolenoid valve 100 and coil 145 of pressure sensor 140 are connected inseries. They are connected to battery voltage Ubat and also to switchingmeans 200. A second terminal of switching means 200 is grounded throughmeasuring means 210. The measuring means is, in the simplest embodiment,an ohmic resistor. The terminals of the battery voltage and the groundcan also be switched around.

Switching means 200 receives triggering signals from a controller 250via conductor 230. At the point of connection between switching means200 and measuring means 210, a signal arrives at controller 250 viaconductor 225. In a similar manner, a signal arrives at controller 250from the second terminal of the measuring means and the ground via aconductor 220.

The inductances, switching means 200, and measuring means 210 can alsobe arranged in a different order in the series between battery voltageUbat and the ground.

The control sends signals SBI to motor control 270 via a conductor 260and receives signals SBS from motor control 270 via conductor 255. Motorcontrol 270 receives signals from various sensors 280. These are, forexample, rotation speed sensors and sensors detecting driver commands.

Based on the output signals of sensors 280, which measure the variousoperating parameters, motor control 270 computes various signals thatdetermine fuel metering. Thus, for example, motor control 270 givescontroller 250 a fuel amount command for the injected amount and asignal that characterizes the start of injection. Controller 250controls, as a function of this signal and any other signals, switchingmeans 200 via control line 230.

Controller 250 analyzes the voltage drop at measuring means 210. Thisvoltage drop is a measure of the current flowing through inductances 105and 145. Based on the variation of the current, the controller detectsthe start of injection SBI and issues a corresponding signal to themotor control. Furthermore, controller 250 detects the point in timewhen the pressure sensor generates a signal indicating that the pressurein element space 110 has exceeded a predefined threshold value.

The variation of the current and the variation of the current derivativeis plotted against time T in FIGS. 3a and FIGS. 3b. The graph of thecurrent and the current derivative is drawn in a highly simplified formin FIGS. 3a and FIGS. 3b.

FIG. 3a shows the variation of the current and FIG. 3b shows thevariation of the time derivative dI/dt over time t.

At time t0, controller 250 issues a signal over triggering line 230, sothat switching means 200 closes and the current flow through inductances105 and 145 is enabled. This results in an increase in the current overtime. The current increase is very steep, which results in a high valuefor the derivative of the current dI/t. At time t1, the solenoid valvechanges its position, i.e., it switches to its closed position. Thisresults in a change in the inductance, which leads to flattening of thecurrent increase.

Starting at time t1, the derivative of the current dI/dt assumes a lowervalue. By analyzing the current variation, for example, by analyzing thederivative of the current over time, time t1 can be determined bycontroller 250. Other methods can also be used for determining time t1.

Closing of solenoid valve 100 results in the pressure increasing inelement space 110. At time t2, the pressure in element space reaches athreshold resulting in a response by the pressure sensor. This meansthat the inductance of coil 145 of the pressure sensor also changes.This results in the pressure increase further flattening and thederivative dI/dt assuming a smaller value.

By analyzing the variation of the current, for example, the derivativeof the current, this time t2 can also be reliably detected bycontrollers 250.

By analyzing the current variation, in particular the derivative of thecurrent, the controller can reliably detect two parameters. These arethe switching time of the solenoid valve, which corresponds to the startof delivery, and the reaching of the threshold value by the pressure,which is a measure for the start of injection.

The variation of current I illustrated in FIG. 3a and the derivative ofthe current dI/dt illustrated in FIG. 3b are given as examples only.Depending on the design of the solenoid valve and the type of thesolenoid and the pressure sensor, other current variations may alsoresult. The common feature of all current variations is that at time T1and time t2, when the solenoid valve 100 assumes its new position (thepressure switch switches), there is a change in the current. Inparticular there is a change in the current increase. This means thatthe derivative of the current dI/dt changes suddenly.

Alternatively it can be provided that the current is regulated to apredefined value. In this case, the voltage applied to the seriesconnection of the inductances changes. By analyzing the voltagevariation, the times of change in the inductances can also be detected.

These times, when the current variation undergoes a change, can bedetected by a multiplicity of procedures, such as those described inDE-OS 34 26 799, for example.

What is claimed is:
 1. A fuel metering system for an internal combustionengine, comprising:an electromagnetic valve having a first inductance,the electromagnetic valve influencing at least one of a beginning offuel metering and an end of fuel metering via a switching; and a sensorhaving a second inductance, the sensor generating a signal indicative ofa status of the metering system; wherein the electromagnetic valve andthe sensor are electrically coupled such that the first inductance andthe second inductance are electrically in series.
 2. The systemaccording to claim 1, wherein the internal combustion engine is aself-igniting internal combustion engine.
 3. The system according toclaim 1, wherein at least one of the first inductance and the secondinductance changes over time.
 4. The system according to claim 1,wherein at least one of a time and a pressure at which the switching ofthe electromagnetic valve occurs is detected as a function of a changein at least one of the first inductance and the second inductance. 5.The system according to claim 1, wherein a current flowing through theelectromagnetic valve and the sensor is measured.
 6. The systemaccording to claim 5, wherein a change in at least one of the firstinductance and the second inductance is detected based on a change in avariation of the current over time.
 7. The system according to claim 1,wherein the sensor is a pressure sensor for sensing a pressure in themetering system.
 8. The system according to claim 1, wherein at leastone of a beginning of injection and the beginning of fuel metering isdetermined.